Sperm Whale
The sperm whale, Physeter macrocephalus, is a marine mammal species, orderCetacea, a toothed whale (odontocete) having the largest brain of any animal. The name comes from the milky-white waxy substance, spermaceti, found in the animal's head. The sperm whale is the only living member of genus Physeter. The synonym Physeter catodon refers to the same species. It is one of three extant species in the sperm whale superfamily, along with the pygmy sperm whale and dwarf sperm whale. A bull can grow to 20.5 metres (67 ft) long. It is the largest living toothed animal. The head can represent up to one-third of the animal's length. It has a cosmopolitan distribution across the oceans. The species feeds on squid and fish, diving as deep as 3 kilometres (9,800 ft), which makes it the deepest diving mammal. Its diet includes giant squid and colossal squid. The sperm whale's clicking vocalization is the loudest sound produced by any animal, but its functions are uncertain. These whales live in groups called pods. Pods of females and their young live separately from older males. The females cooperate to protect and nurse their young. Females give birth every three to six years, and care for the calves for more than a decade. Historically, the sperm whale was also known as the common cachalot; "cachalot" is derived from an archaic French word for "tooth". Over most of the period from the early 18th century until the late 20th century, the sperm whale was hunted to obtain spermacetiand other products, such as sperm oil and ambergris. Spermaceti found many important uses, such as candles, soap, cosmetics and machine oil. Due to its size, the sperm whale could sometimes defend itself effectively against whalers. In the most famous example, a sperm whale attacked and sank the American whaleship [http://en.wikipedia.org/wiki/Essex_%28whaleship%29 Essex] in 1820. As a result of whaling, the sperm whale is currently listed as vulnerable by the IUCN. The sperm whale has few natural predators, since few are strong enough to successfully attack a healthy adult; orcas attack pods and kill calves. The sperm whale can live for more than 70 years. Size The sperm whale is the largest toothed whale, with adult males measuring up to 20.5 metres (67 ft) long and weighing up to 57,000 kilograms (56 LT; 63 ST).[4][10] By contrast, thesecond largest toothed whale, Baird's Beaked Whalemeasures 12.8 metres (42 ft) and weighs up to 15 short tons (14,000 kg).[11] It is among the most sexually dimorphic of all cetaceans. At birth both sexes are about the same size,[9] but mature males are typically 30% to 50% longer and three times as massive.[4] Appearance The sperm whale's distinctive shape comes from its very large head, which is typically one-third of the animal's length. Theblowhole is located very close to the front of the head and shifted to the whale's left.[4] This gives rise to a distinctive bushy, forward-angled spray. The sperm whale's flukes are triangular and very thick. The whale lifts its flukes high out of the water as it begins a dive.[4] It has a series of ridges on the back's caudal third instead of a dorsal fin. The largest ridge was called the 'hump' by whalers, and can be mistaken for a dorsal fin because of its shape.[9] In contrast to the smooth skin of most large whales, its back skin is usually knobbly and has been likened to a prune by whale-watching enthusiasts.[12] Skin is normally a uniform grey in color, though it may appear brown in sunlight. Albinos have also been reported.[13][14][15] Jaws and teeth The sperm whale has 20 to 26 teeth on each side of its lower jaw.[4] The teeth are cone-shaped and weigh up to 1 kilogram (2.2 lb).[16] The purpose of the teeth is unknown. Teeth do not appear to be necessary for capturing or eating squid, and well-fed animals have been found without teeth. One hypothesis is that the teeth are used in aggression between males.[17]Bulls often show scars which seem to be caused by the teeth. Rudimentary teeth are also present in the upper jaw, but these rarely emerge into the mouth.[18] Respiration and diving Sperm whales, along with bottlenose whales and elephant seals, are the deepest-diving mammals.[4] Sperm whales are believed to be able to reach 3 kilometres (1.9 mi) and remain submerged for 90 minutes.[4][19] More typical dives are around 400 metres (1,300 ft) and 35 minutes in duration.[4] At these great depths, sperm whales sometimes become entangled in transoceanic telephone cables and drown.[20] The sperm whale has adapted to cope with drastic pressure changes when diving. The flexible ribcage allows lung collapse, reducing nitrogen intake, and metabolism can decrease to conserve oxygen.[21][22] Myoglobin, which stores oxygen in muscle tissue, is much more abundant than in terrestrial animals.[23] The blood has a high red blood celldensity, which contain oxygen-carrying hemoglobin. The oxygenated blood can be directed towards the brain and other essential organs only when oxygen levels deplete.[24][25][26] The spermaceti organ may also play a role by adjusting buoyancy (seebelow).[27] While sperm whales are well adapted to diving, repeated dives to great depths have long term effects. Bones show pitting that signals decompression sickness in humans. Older skeletons showed the most extensive pitting, whereas calves showed no damage. This damage may indicate that sperm whales are susceptible to decompression sickness, and sudden surfacing could be lethal to them.[28] Between dives, the sperm whale surfaces to breathe for about eight minutes before diving again.[4] Odontoceti (toothed whales) breathe air at the surface through a single, S-shaped blowhole. Sperm whales spout (breathe) 3–5 times per minute at rest, increasing to 6–7 times per minute after a dive. The blow is a noisy, single stream that rises up to 2 metres (6.6 ft) or more above the surface and points forward and left at a 45° angle.[29] On average, females and juveniles blow every 12.5 seconds before dives, while large males blow every 17.5 seconds before dives.[30] Brain and sense The brain is the largest known of any modern or extinct animal, weighing on average about 8 kilograms (18 lb),[33][34] though the sperm whale has a lower encephalization quotient than many other whale anddolphin species, lower than that of non-human anthropoid apes, and much lower than humans'.[34][35] Like other toothed whales (suborder odontoceti), sperm whales useecholocation as one means to find food because their habitat has favorable acoustic characteristics, and light absorption by water andsuspended material limits visual range. The whale emits a focused wide angle beam of high-frequency clicks. Passing air generates sounds from the bony nares through the phonic lips (also known as "monkey lips"), a structure within the head.[31] The skull, melon, and various air sacs in the whale's head all play important roles in forming and focusing the beam of sound. The lower jaw is the primary echo reception path. A continuous fat-filled canal transmits received sounds to the inner ear.[32] Reproduction Sperm whales can live 70 years or more.[9][13][45] They are a prime example of a species that has been K-selected, a reproductive strategy associated with stable environmental conditions, a low birth rate, significant parental aid to offspring, slow maturation, and high longevity.[4] How they choose mates has not been definitively determined. There is evidence that males have dominance hierarchies, and there is also evidence that female choice influences mating.[46] Gestation requires 14 to 16 months, producing a single calf.[9]Lactation proceeds for 19 to 42 months, but calves may suckle up to 13 years (although usually less).[9] Calves can suckle from females other than their mothers.[9] Females generally have birth intervals of three to six years.[9] Females reach sexual maturity between 7 and 13 years; males follow beginning at 18 years. Upon reaching sexual maturity, males move to higher latitudes, where the water is colder and feeding is more productive. Females remain at lower latitudes.[9] Males reach their full size at about age 50.[4] Social behavior Females stay in groups of about a dozen individuals and their young.[4] Males leave these "nursery pods" at somewhere between 4 and 21 years of age and join a "bachelor pod" with other males of similar age and size.[4] As males grow older, they tend to disperse into smaller groups, and the oldest males typically live solitary lives.[4] Mature males have beached themselves together, suggesting a degree of cooperation which is not yet fully understood.[4] The most common non-human attacker of sperm whales is the orca, but pilot whales and the false killer whale also sometimes attack or harass them.[47][48] Orcas target groups of females with young, usually trying to extract and kill a calf. Female sperm whales repel these attacks by encircling their calves. The adults either face inwards to use their tail flukes against the orcas, or outwards, fighting with their teeth.[4] This margueriteformation, named after the flower, is also used by whales to support an injured pod member. Early whalers exploited this behaviour, attracting a whole pod by injuring one of its members.[49] If the orca pod is extremely large, its members may sometimes be able to kill adult female sperm whales. Large bull sperm whales have no non-human predators, and are believed to be too large and strong to be threatened by orcas.[50] Feeding Sperm Whales usually dive between 300 to 800 metres (980 to 2,600 ft), and sometimes 1–2 kilometres (3,300–6,600 ft) to search for food.[51] Such dives can last more than an hour.[51] They feed on several species, notably the giant squid, the colossal squid,octopuses, and diverse fish like demersal rays, but the main part of their diet consists of medium-sized squid.[52] Some prey may be taken incidentally while eating other items.[52] Most of what is known about deep sea squid has been learned from specimens in captured sperm whale stomachs, although more recent studies analysedfecal matter. One study, carried out around the Galápagos, found that squid from the genera Histioteuthis (62%), Ancistrocheirus (16%), and Octopoteuthis (7%) weighing between 12 and 650 grams (0.026 and 1.4 lb) were the most commonly taken.[53] Battles between sperm whales and colossal squid (which have been measured to weigh nearly 500 kilograms (1,100 lb)) have never been observed by humans; however white scars are believed to be caused by the large squid. One study published in 2010 collected evidence that suggests that female sperm whales may collaborate when huntingHumboldt squid.[54] An older study, examining whales captured by the New Zealand whaling fleet in the Cook Strait region, found a 1.69:1 ratio of squid to fish by weight.[55] Sperm whales sometimes steal Sablefish and Toothfish from long lines. Long-line fishing operations in the Gulf of Alaska complain that sperm whales take advantage of their fishing operations to eat desirable species straight off the line, sparing the whales the need to hunt.[56] However, the amount of fish taken is very little compared to what the sperm whale needs per day. New video footage has been captured of a large male sperm whale "bouncing" a long line, to gain the fish.[57] Sperm whales are believed to prey on the megamouth shark, a rare and large deep-sea species discovered in the 1970s.[58] In one case, three sperm whales were observed attacking or playing with a megamouth.[59] The sharp beak of a consumed squid lodged in the whale's intestine may lead to the production of ambergris, analogous to the production of pearls.[60] The irritation of the intestines caused by squid beaks stimulates the secretion of this lubricant-like substance. Sperm whales are prodigious feeders and eat around 3% of their body weight per day. The total annual consumption of prey by sperm whales worldwide is estimated to be about 100,000,000 short tons (91,000,000 t) — a figure greater than the total consumption of marine animals by humans each year.[61] It is not well understood why the sperm whale's head is so large in comparison to the lower jaw. One theory is that the sperm whale's ability to echolocate through its head aids in hunting. However squid, its main prey, may have acoustic properties too similar to seawater to reflect sounds.[62] The sperm whale's head contains a structure called monkey lips, through which it blows air. This can create clicks that have a source level exceeding 230 decibels re 1 micropascal referenced to a distance of 1 metre (3.3 ft) – in other words it is by far the loudest sound made by any animal, and 10–14 dB louder than a powerful rifle sounds in air at 1 metre (3.3 ft) away.[63] It has been hypothesised that clicks attempt to stun prey. Experimental studies attempting to duplicate this effect have been unable to replicate the supposed injuries, casting doubt on this idea.[64]